What is the cause of welding embrittlement of 304 stainless steel pipe?

304 stainless steel pipes are prone to cracking of welded joints during welding. The fundamental reason for this is that during the welding process, martensitic stainless steel may be transformed into a cast structure and cementite may be precipitated, or the crystals may become coarse and a small amount of metallographic structure may be formed, which may reduce the plasticity and ductility of seamless welded joints.

There are two ways to prevent cracking of stainless steel bright pipe welded joints: use low welding line energy and fast cooling rate, and use the lowest possible welding ratio. In addition to being prone to brittleness, welded joints are also prone to intergranular corrosion cracking. There are many reasons for this, and the main ones related to welding are residual stress and joint structure. On the one hand, due to the low heat transfer coefficient and large thermal expansion coefficient of martensitic stainless steel, very large internal stress will be generated during welding. The emergence of thermal stress is one of the necessary conditions for intergranular corrosion cracking.

Therefore, the following measures should be taken to prevent intergranular corrosion cracking. The first is to adjust the welding composition, which is also one of the key methods to improve the intergranular corrosion resistance of the joint; the second is to reduce or eliminate the residual stress of welding, through the design of the welding structure, minimize the constraint of the joint, efficiently arrange the welding sequence, and do a good job of eliminating the internal stress after welding; the third is to improve the surface condition of the 304 stainless steel pipe, such as shot peening the surface of the sensitized side, or polishing, electroplating or painting the sensitized surface to improve the corrosion resistance; the fourth is to use efficient welding technology, such as adopting the welding method of heat source collection, small linear kinetic energy and rapid cooling treatment to reduce the precipitation of cementite and prevent the joint structure from overheating.

GNEE supplies 304 stainless steel pipes with diameters from DN15 (1/2") to DN3000 (120"), wall thickness grades from SCH5S to SCH160, and materials covering various grades: carbon steel, stainless steel, duplex stainless steel/super duplex steel, etc.